It has long been recognized that most mammals and in particular humans exhibit distinct recurring electrical frequencies in their brain wave patterns, each of which is related to separately identifiable physiological states. Brain waves having dominant frequencies from approximately 8-13 Hz, inclusive, are known as Alpha frequency brain waves and are associated with relaxed and meditative states as would occur when a subject has his eyes closed but is conscious and not thinking.
Techniques and devices which attempt to promote natural relaxation may be generally classified as passive or active. Passive devices serve merely to mask out irritating external noises with more pleasant sounds or utilize random or "white noise" to psychologically distract the subject from events which inhibit natural relaxation. Active devices seek to intentionally induce Alpha frequency brain waves in the subject, a phenomena known as "brain driving". Irrespective of the manner in which such brain waves are induced, a subject whose brain waves are principally in the Alpha frequency range will become deeply relaxed and exhibit the same beneficial reduced muscular tension and lowered anxiety and adrenalin levels as are associated with a naturally occurring state of relaxation.
Typical of the numerous passive devices are those which vary the output signal from a "white noise" source and convert the same to an accoustical signal, resulting in pleasant masking sounds. In one device, the white noise source output has its amplitude varied by a saw tooth wave form to produce sounds similar to waves repeatedly breaking in a surf. In another device, the output signal from a "white noise" source has its spectral content and amplitude varied in direct response to a subject's instantaneous dominant brain wave frequency and amplitude, respectively, producing a feedback signal to be utilized by the subject to recognize his present physiological state. All passive devices suffer from a fundamental inadequacy in that they cannot actually induce Alpha frequency brain waves with its associated relaxed and meditative condition.
Currently only three basic techniques for forcing a subject into a state exhibiting Alpha frequency brain waves are known to exist. Perhaps the most widely used is chemical tranquilizers, always subject to potentially grave known and unknown negative side effects or contraindications. The other techniques for "brain driving" involve the use of very bright, quickly flashing lights, direct electrical pulse stimulation of the brain through skin electrodes, or some combination thereof. In either instance, the lights or electrical pulses are synchronized to occur at a rate within the Alpha frequency range, i.e., from about 8 to 14 Hz. However, such flashing lights are not only irritating but may likely initiate a seizure in epileptic individuals. Electrical pulses are not only irritating, but also may produce unknown, deleterious side effects upon other parts of the brain or other neurological activity. Moreover, these devices attempt to very abruptly force the subject from an active and possibly highly emotional state to a highly relaxed and meditative state, thereby greatly increasing the likelihood of failure.